Radiation scanner systems that are used to detect foreign objects and contaminants in food products and pharmaceutical products belong to the known state of the art. For the protection of personnel in the proximity of the equipment, the radiation in a scanner system of this type needs to be contained inside an enclosure cabinet which can be divided into an infeed compartment, a radiation inspection compartment, and an outfeed compartment. A belt conveyor which is normally part of the system and is arranged inside the enclosure cabinet carries the arriving articles through the infeed compartment, through the radiation inspection compartment, and through the outfeed compartment. In the radiation inspection compartment, an X-ray generator is arranged at some distance above the conveyor belt, while a radiation detector is arranged immediately underneath the top portion of the conveyor belt, i.e. vertically in between the forward moving section and the return section of the conveyor belt loop. Thus, an article travelling on the conveyor belt is traversed by the radiation from the radiation generator above the belt, and the rays transmitted by the article and the belt are received by the radiation detector below the top section of the belt.
Such a system normally includes or is operatively connected to a rejection mechanism which is arranged downstream of the radiation inspection compartment and serves to remove articles that were found to contain foreign objects or contaminants, so that the stream of articles continuing down the line contains only acceptable articles. The rejection mechanism causes the rejected articles to be moved off the conveyor belt into a reject bin where they are collected for further investigation, disposal or other special treatment.
The conveyor belt is typically made of a flexible polymer material. It must be easily accessible for cleaning as well as easy to uninstall and reinstall for maintenance and replacement. Since the belt is of a seamless closed-loop configuration, the requirement for easy uninstallation and reinstallation poses certain design challenges which have been addressed in known designs of the prior art.
For example in a conveyor belt arrangement proposed in JP 3867209 B2, only one end of each belt roller is supported by a bearing, so that the belt rollers can be compared to cantilever arms. After opening an enclosure door and loosening a belt-tensioning device, the belt can be pulled off the free end of the belt rollers. As an area of concern with this concept of cantilevered belt rollers, the transverse and friction forces in the bearings of the belt rollers would be bigger by an order of magnitude than they are in a conventional belt conveyor with bearings at both ends of each roller axle. This would necessitate the use of larger and stronger bearings which would have to be mounted in a commensurately solid and massive one-sided supporting structure of the conveyor belt.
In another arrangement which is described in U.S. Pat. No. 6,512,812 B2, the conveyor bed with the X-ray detector is configured as an integral X-ray detection unit, i.e. a subassembly within the enclosure cabinet, which can be taken out for cleaning, maintenance or belt exchange.
The applicant of the present invention manufactures radiation inspection systems wherein both the infeed compartment and the outfeed compartment are configured analogous to the air locks that are used for clean rooms. The entrance into the infeed compartment, the interior passages from the infeed compartment to the radiation inspection compartment and from the radiation inspection compartment to the outfeed compartment, as well as the exit from the outfeed compartment are protected by shielding curtains. Such shielding curtains are commonly configured as vertically slit sheets of rubber or of a rubber-like material containing a radiation-blocking component such as lead oxide or tungsten, for example as a sandwiched laminate or in distributed form. An entire shielding curtain can consist of a single sheet, but typically a close coupled pair of sheets is used with the slits of one sheet offset against the slits of the other, so as to minimize the radiation leakage through the curtain.
In a radiation inspection system of the kind just described, the rejection mechanism can be conveniently arranged inside the outfeed compartment and the reject bin can be configured as an expanded lateral portion of the outfeed compartment. By utilizing the space inside the outfeed compartment, this arrangement allows an efficient, space-saving layout with a compact foot print. As mentioned above in the context of the prior art, the layout of the radiation inspection system should be such that the conveyor belt is easily accessible for cleaning as well as easy to uninstall and reinstall for maintenance and replacement. Preferably, the access to the conveyor belt should be from a front side of the radiation inspection system, i.e. the same side where the reject bin is located and is opened for emptying. In particular, it should be possible to take the conveyor belt out of the enclosure cabinet by removing or opening only one enclosure door or enclosure panel on the front side of the radiation inspection system and to pull the belt off its rollers in a frontward direction.
However, the arrangement of the reject bin on the front side, which is also the preferred access side for cleaning, servicing and exchanging the conveyor belt, represents a serious obstacle to the realization of the foregoing layout concept. The reject bin normally restricts the ability to remove and replace the belt due to fixed physical obstructions which are in the belt removal path and which are typically needed to comply with regulatory limits for radiation leakage and to meet the requirements of safe mechanical machine design. Consequently, the belt removal according to current methods is either accomplished from the opposite side of the reject bin assembly, or the reject bin assembly must be electrically and mechanically disconnected and removed to accomplish the task. The latter method requires the physical removal of all or portions of the bin which, in turn, causes machine down-time and loss of productivity.
The object of the present invention is therefore to provide an in-line radiation inspection system of the foregoing description, wherein the conveyor belt can be accessed for cleaning, servicing and belt exchange from the same side of the machine where the reject bin is located, and wherein the conveyor belt can be removed from the enclosure cabinet without having to dismantle all or part of the reject bin.